As a method of bonding electrodes arranged on a substrate and core wires of covered conductor wires disposed to an electronic component, a method of using a soldering iron has been known. In the method of bonding electrodes and core wires by using a soldering iron, solder heat-melted by the soldering iron is supplied to an overlapped portion of the electrode and the core wire and then the solder is cooled to solidify to bond the electrode and the core wire mechanically and electrically (Patent Document 1).    [Patent Document 1] Japanese Unexamined Patent Publication JP-A-9-57436